The present invention relates to computed tomography machines, and in particular to a gantry support structure allowing scanning of stationary patients.
Computed tomography (CT), and in particular computer x-ray tomography, is an imaging technique that may generate cross-sectional images of a patient by mathematically combining multiple x-ray images (projections) taken along the plane of the cross-section at a range of angles.
In fan beam CT, the x-rays used to acquire the projections are collimated to a thin fan beam lying within the plane of the cross-section and received by a narrow linear detector. The combination of the x-rays to a fan beam permits data acquisition with substantially reduced x-ray scatter, in turn providing improved image fidelity in the cross-sectional or tomographic image when compared to a comparable CT system using a cone beam of x-rays measured with an area detector array.
Generating a tomographic image normally requires a projection set of multiple projections over at least 180 degrees and preferably 360 degrees of angular range about the patient. The patient may be moved through a gantry holding an x-ray source and x-ray detector as they turn in opposition about the patient to acquire each x-ray projection set, either continuously during the orbital motion (helical scanning) or step-wise in between orbits (step scanning) to obtain x-ray projection sets for adjacent cross-sectional images that together describe a volume of tissue. Movement of the patient may be provided by supporting the patient supine on a horizontally extending radio translucent table that may move through the gantry.
The fan beams may generate cross-sectional images of “slices” that may be as thin as a few millimeters. Generating tomographic data for a significant volume of tissue in a reasonable time therefore requires rapid movement of the x-ray tube and detector in many orbits. For this reason CT acquisition normally use a specialized gantry system having a housing internally supporting the x-ray tube and detector on a bearing system for continuous or near continuous rotation about an unobstructed bore volume. This gantry system is readily distinguishable from typical C-arm systems used, for example, for general-purpose x-ray imaging and cone beam CT where only one or few orbits of the patient is required.
CT imaging of some patients may preferably be performed with the patient in a standing position. For example, a lung cancer patient undergoing thoracic radiotherapy may prefer to be in a standing position so as not to promote the coughing that often accompanies this treatment. Some medical conditions such as vertebral fractures may be more evident in a weight-bearing standing position.
Conventional CT systems employing a horizontally extending table generally prevent practical use of CT machines for large animals such as horses. While specialized tables may be constructed for horses, for example, as described in U.S. Pat. No. 8,505,137, positioning a large animal on such a table requires induction of general anesthesia, which substantially increases the amount of time required to obtain a scan.